Painting Aluminum

[sigsignman]

I have a client whos non illuminated sign cabinets were damaged and will require new retainers on 4 signs. What is the best process to paint raw aluminum channel? Do you use a self-etching primer, prime, then paint? Can it be done without skuffing or sanding? Any suggestions and paint system names would be helpful. thank you!

David Holland

 

[Scotchbrite]

We always sand before painting. Etching primer, then paint. We use Matthews Acrylic Polyurethane.

 

[signbrad]

We always sand before painting. Etching primer, then paint. We use Matthews Acrylic Polyurethane.

Sanding and etching aluminum is important for adhesion. It is also good to do a solvent wash prior to sanding. Sometimes contaminants can be ground into the metal by the sanding process. After sanding, I do a second solvent wash, and then a tack cloth, before using one of the Matthews acid etch primers (PT Filler or HBPT).
PT Filler does a pretty good job of filling 150 grit sanding scratches. Always apply two double-wet spray coats. Apply the second coat before the first is completely dry. HBPT is heavier-bodied. Two double-wet coats achieves the recommended film thickness.
As soon as it's air dry you can topcoat.

If you must brush the primer, an autobody supply may have an acid wash primer that can be applied without spray equipment.

If you can't find an acid primer, an epoxy primer will work once the aluminum is thoroughly cleaned and sanded.

Brad in Kansas City

 

[Notarealsignguy]

We sand it, blast it or etch with white vinegar then epoxy. I wouldn't rely strictly on an etch primer without abrading the material. Most epoxies today can be applied to properly etched aluminum so wash primers are going to the wayside somewhat.

 

[Gino]

Most of our stuff is powder coated. Not sure how the initially clean it, but it holds up for a very very long time.

 

[Notarealsignguy]

They acid wash it before powder coating.

 

[Gino]

I guess that's a good thing. Sounds way better than all these other methods.

Does anybody still do a spit-shine ??

 

[sigsignman]

thanks for the information Very helpful. I will let my paint guy know this

 

[VizualVoice]

So for my other business I prep, paint and then apply hydrographics to several hundred pieces of raw aluminum each month. Aluminum needs to be etched for proper adhesion, scuffing or sanding or even sandblasting works, but you know what else does? Lye, which happens to be the main ingredient in Purple Power degreaser. On a nice warm day, a jug of PP and a hudson sprayer will do wonders for them. Keep them wet for about 15 min (watch for the color to change to a dark gray) then hose off. Once dry the will have a light dusting of white powder (aluminum oxide) that can be easily removed with a maroon scotchbrite pad. Once that's done, a quick solvent wipe (I use automotive reducer), and then a coat of automotive epoxy primer and you'll have great adhesion for either your base coat/clear coat, or single-stage catalyzed paint. Hope that helps. If you have other questions feel free to ask.

 

[Notarealsignguy]

I was always told you do a basic wash (the degreaser) and then an acid etch. If you etch with vinegar, you don't have to scotch bright. You also shouldn't use reducer to do your prep, it's too hot and can cause sand swelling and paint lifting.

 

[VizualVoice]

I was always told you do a basic wash (the degreaser) and then an acid etch. If you etch with vinegar, you don't have to scotch bright. You also shouldn't use reducer to do your prep, it's too hot and can cause sand swelling and paint lifting.

I've not tried vinegar, but suspect it to be too mild of an acid to really get a good surface profile on the aluminum. I could be wrong, but that's my gut feeling.

The purple power does a great job of degreasing AND if left on longer will also etch to a great profile for paint adhesion.

As far as not using reducer, I'm confused by your comment. What do you mean "sand swelling"? And it's thoroughly dry before I prime them so not sure why it would cause lifting since it's not leaving a residue.

 

[Notarealsignguy]

I've not tried vinegar, but suspect it to be too mild of an acid to really get a good surface profile on the aluminum. I could be wrong, but that's my gut feeling.

The purple power does a great job of degreasing AND if left on longer will also etch to a great profile for paint adhesion.

As far as not using reducer, I'm confused by your comment. What do you mean "sand swelling"? And it's thoroughly dry before I prime them so not sure why it would cause lifting since it's not leaving a residue.

It's just not good practice to wipe down with reducer. Wax and grease remover, denatured alcohol etc is what you should be using. I've never heard of anyone using a basic cleaner to etch aluminum for paint prep. Standard practice is an acid etch. I don't know for sure but I'd venture to say that your purple power corrodes the aluminum where an acid will remove it.

 

[Medina Signs]

I agree with Brad - we would sand and clean, use Matthews etch primer and then overcoat - problem is that Matthews is back ordered on a lot of products. At this point, there are rattle cans of aluminum primer in supply and then top coat with another rattle can. We will use rattle cans on small stuff - I guess I would qualify retainers as small stuff. You're okay with Black and White, other colors to match the cabinet may be tricky and then you are back to mix paint.

 

[visual800]

scuff it clean it spray it with 2 part epoxy and then topcoat with matthews OR latex

 

[Mr. Signboy]

If you use a decent enough etch primer you probably don't have to sand it as long as it's cleaned well. I would do it right though, sand everything or at the very least use red scotchbrite, etch any spots that metal show through if it's already painted.